Quasi-static magnetic measurements to predict specific absorption rates in magnetic fluid hyperthermia experiments

Abstract

In this work, the issue on whether dynamic magnetic properties of polydispersed magnetic colloids modeled using physical magnitudes derived from quasi-static magnetic measurement can be extrapolated to analyze specific absorption rate data acquired at high amplitudes and frequencies of excitation fields is addressed. To this end, we have analyzed two colloids of magnetite nanoparticles coated with oleic acid and chitosan in water displaying, under a radiofrequency field, high and low specific heat power release. Both colloids are alike in terms of liquid carrier, surfactant and magnetic phase composition but differ on the nanoparticle structuring. The colloid displaying low specific dissipation consists of spaced magnetic nanoparticles of mean size around 4.8 nm inside a large chitosan particle of 52.5 nm. The one displaying high specific dissipation consists of clusters of magnetic nanoparticles of mean size around 9.7 nm inside a chitosan particle of 48.6 nm. The experimental evaluation of Néel and Brown relaxation times (∼10−10 s and 10−4 s, respectively) indicate that the nanoparticles in both colloids magnetically relax by Néel mechanism. The isothermal magnetization curves analysis for this mechanism show that the magnetic nanoparticles behave in the interacting superparamagnetic regime. The specific absorption rates were determined calorimetrically at 260 kHz and up to 52 kA/m and were well modeled within linear response theory using the anisotropy density energy retrieved from quasi-static magnetic measurement, validating their use to predict heating ability of a given polydispersed particle suspension. Our findings provide new insight in the validity of quasi-static magnetic characterization to analyze the high frequency behavior of polydispersed colloids within the framework of the linear response and Wohlfarth theories and indicate that dipolar interactions play a key role being their strength larger for the colloid displaying higher dissipation, i.e., improving the heating efficiency of the nanoparticles for magnetic fluid hyperthermia.

Effects of Nanostructure and Dipolar Interactions on Magnetohyperthermia in Iron Oxide Nanoparticles

“…The SAR depends on different intrinsic properties of the nanoparticles (volume, anisotropy, and saturation magnetization, for example), external field conditions (frequency and amplitude), and colloidal properties during the experiments, such as solvent viscosity and concentration, which modulate the magnetic dipolar interactions or possible nanoparticle agglomerations or assembly. − Different experimental studies were recently carried out to try to understand and determine the crossover between individual and collective effects on colloidal SAR experiments. The results indicate that the effect of dipolar interaction or agglomerations needs to be considered for colloids above certain concentrations. − …”

Experimental estimation and analysis of variance of the measured loss power of magnetic nanoparticles

“…Despite continuing debate, calorimetry continues to be the most common method to estimate the SLP 11 , 18 , 19 . The method is deceptively straightforward: heat generated by a magnetic nanoparticle suspension when exposed to an AMF is related to loss power through measured temperature change.…”

Effect of Nanoclustering and Dipolar Interactions in Heat Generation for Magnetic Hyperthermia

“…Heat dissipation under a radio-frequency (RF) field of an ensemble of homogeneously dispersed nanoparticles has been widely studied from theoretical − and experimental − points of view. However, how MNPs belonging to a nanocluster behave magnetically in a highly interactive environment and how this behavior influences their heating efficiency are still open questions.…”